While a tire tread is designed to be in contact with the ground surface and is therefore constructed from compositions intended for this purpose, the sidewalls are generally not designed to be ground contacting. Instead, the sidewalls of a tire typically include a layer of rubber material that covers certain structural elements, such as e.g., the cords of a tire carcass, which extend between and through the sidewalls of the tire. This rubber material is conventionally created from a composition not designed for ground contact but rather for flexibility so that the sidewalls can withstand the repeated flexing of the tire that occurs as it rotates through the contact patch. In addition, this sidewall rubber is typically not as thick as the tread rubber. As such, the sidewalls generally have less resistance than the tread to puncture damage that can occur when the tire is contacted with another object in or along the ground surface.
Certain tires are intended for more rugged applications where encounters with objects that may puncture or otherwise damage the sidewall can be frequent. For example, for recreational and emergency off-road applications, tires may be subjected to contact with rocks, trees, and other objects that can puncture and deflate a pneumatic tire. Of course, for such tires it is generally desirable to increase their capability to resist sidewall aggression—i.e., to increase their resistance to puncture, rupture, or other sidewall damaging events caused by contact during tire use. Features can be added at, for example, the shoulder region of the tire to help resist certain sidewall aggressions. More particularly, lugs or blocks can be added about the shoulder to protect the sidewall from shoulder aggression by remaining between a dangerous object and the sidewall as the tire rolls over the object.
While testing tires under actual conditions such as off road environments can provide important information about a tire's ability to resist sidewall aggression, the repeatability of such testing in harsh conditions so that different tires may be compared accurately is very difficult. Even operating the same vehicle over the same path of rocky terrain does not ensure that the tires will be subjected to the same sidewall aggression events on each pass. Rocks and other debris can be moved or affected by each pass of the vehicle, thereby ensuring that different conditions will be presented even if the vehicle can be operated along the same path for each pass. A rock that does not present a sharp point during one pass may be repositioned in a manner that becomes more of a sidewall damage threat for the next pass or vice versa. As such, it can be difficult to compare different tires with such testing.
Accordingly, specific methods for testing a tire's ability to resist damage from sidewall aggression are desirable. More particularly, methods for determining particular performance parameters that characterize a tires resistance to sidewall aggression under conditions that can be repeated among multiple tests would be very useful. These and other useful aspects of the present invention will be apparent from the description that follows.